FIG. 1 of the attached drawing shows a simplified block diagram of the GSM mobile communications system. The mobile station MS is connected via a radio path to a base transceiver station BTS, in FIG. 1 to the base station BTS1. A base station sub-system BSS consists of a base station controller BSC and the base stations BTS controlled by it. A mobile services switching center MSC usually controls several BSC and is connected to other mobile services switching centers and a GMSC (Gateway Mobile Services Switching Center). Via the GMSC, the GSM network is connected to other networks, such as the PSTN (Public Service Telephone Network), another mobile communication network (PLMN), or the ISDN network. The operation of the entire GSM system is monitored by the operation and maintenance center OMC. Subscriber data is stored in the Home Location Register HLR and in the Visitor Location Register VLR.
In a data communications system, network and mobile terminal functionality can be observed by tracing. A tracing facility enables the network to trace the activities of various entities when specific events occur within the system. The tracing facility enables the tracing of all the information that is available to the network concerning the call path. Examples of information that could be in a trace record are the identity of the originating and terminating equipment of the subscriber, supplementary services invoked, and all A-interface messages. The tracing facility can be used during system testing and commissioning, for example. In particular it may be used in conjunction with test mobile stations to confirm the network integrity and also the network quality of service (QoS). The facility may be used for subscriber observation, e.g. following a customer complaint or when the operator suspects malfunction of equipment, or at the request of the police. An example of equipment malfunction is the failure of handovers. Furthermore, tracing makes it possible for the network to define a particular subscriber's location with the accuracy of a base station, for example.
Tracing can be divided into subscriber tracing, i.e. the tracing of the International Mobile Subscriber Identity IMSI, and equipment tracing, i.e. the tracing of the International Mobile station Equipment Identity IMEI. IMEI may be traced in order to find out the current IMSI, or the location or behavior of faulty or stolen equipment when reported via the EIR (Equipment Identity Register).
Trace activation is performed at the initiative of an operator by the switching center MSC to allow a trace record to be produced for a particular IMSI or IMEI when an invocation event occurs. Tracing is invoked by sending a BSSMAP MSC_INVOKE_TRACE message from the MSC to the BSS. The invocation event could be a location update, a call set-up, a handover, and/or a SMS (Short Message Service), for example. Trace records are generated according to the trace type given at trace activation. The trace type describes the invoking events for which the operator wishes to collect a trace record for a particular IMSI or IMEI and the type of record to be collected, i.e. the information needed. When a subscriber undertakes such action as to cause an invoking event to start, the compilation of a trace record commences according to the trace type. The trace is deactivated by the operator at the MSC using a special management function. Deactivation also occurs when the subscriber leaves the network service area or when a certain time limit is met. Network elements can limit the number of simultaneous traces by either rejecting a trace request or by only producing a sub-set of the information required.
The problem with the above described tracing facility according to prior art is that activation as well as deactivation of the tracing is done manually at the switching center MSC by the operator. This causes extra load for network management thus making the use of the tracing facility difficult. Furthermore, the activated trace is on until it is deactivated and might be recording unnecessarily when deactivation has not occurred in due time. For example, test mobile stations of the maintenance personnel are usually traced continuously although this would be desirable for only part of the time. This useless tracing causes excessive load to the MSC and the OMC and unduly restricts the number of terminals that can be traced. Yet another problem with the prior art tracing facility is that the numbers to be traced have to be set manually in advance and due to the load caused to the network by tracing, the number of these numbers set to be traced is usually limited.